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Pres HR2510 - What a Mess!

Discussion in 'CB Radio Modifications' started by Robb, Feb 5, 2018.

  1. Robb

    Robb Yup

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    I don't normally get to work on these fine, old radios. But one came to me just the other day from a local trucker op that brings me his radios from time to time.

    The amount of glue that holds the toroids in the back of the radio is daunting to remove. However, I have found that using the soldering iron will soften it up really fast and w/o damaging the board or the parts themselves. Makes removal from the board much easier. Problem is: what do I use to remove the glue from the toroid after it is out? Another problem: what kind of glue can I use to refasten it to the board that won't become conductive? Epoxy? Certainly not hot glue?!? I know; old clewing gum obtained from the bottom of a restaurant table?!?
    lol . . .



    Also had a problem with the heat sink getting too hot And something I have NEVER seen before: the speaker was getting so hot you couldn't keep your hand on it - and still worked!.

    Turned out the MRF-477 had perished. Could it be because the person that installed it left out the mica insulator?!?

    No doubt that it will need to get re capped. But there are nearly ~70 electrolytics on board. Figuring that replacing 15 caps/hour/average would mean close to/exceeding four and a half hours labor. Not to mention the fact that the cap kit will be nearly twice the price. Doesn't add up to a cheap bill. Gonna have to break the news to the customer. Guesstimate the bill will be $40 for the caps, $90 for cap replacement/labor, another $45 for a MRF-497MP (replaces the MRF-477 and can be purchased from 'RF Parts'). Then alignment will be another $50. That's 225 buckereenies w/o anything else it might yet need. If I charge for glue removal (I should); that will be another $30.

    Nice old radio; but not a cheap date by any means!
     
    #1 Robb, Feb 5, 2018
    Last edited: Feb 6, 2018
    Shadetree Mechanic likes this.

  2. nomadradio

    nomadradio Analog Retentive

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    No, not a cheap date.

    The MRF477 is not wired like the japanese CB final transistors. The center leg is the emitter, and so is the mounting tab. It was grounded directly to the heat sink without any insulating washer from the factory.

    73
     
    bob85, Robb and sp5it like this.
  3. Robb

    Robb Yup

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    Thanks. Yeah; I suspected that was the reason.

    What about the glue situation?
    Am I charging too little for the time?
     
  4. nomadradio

    nomadradio Analog Retentive

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    Had good luck with toluene on that glue. Just don't turn the radio into a mushroom cloud. Mucho flammable.

    We have been using DAP contact cement to anchor the toroid. Just takes a while to harden.

    If you're not calculating the labor bill by the minute, you're probably undercharging them for that project.

    Got tired of wasting time fixing microphones that would work until you put it back together. My rate is now a buck and a half a minute, elapsed time for mike repair. I tell them it's like taking a taxi to the airport. If you run out of money two blocks from the airport, you get out and walk the rest of the way.

    Or like calling a plumber. If the pipe still leaks after he works for two hours, you owe him for two hours' labor just the same.

    73
     
    LeapFrog and Robb like this.
  5. Klondike Mike

    Klondike Mike Well-Known Member

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    My capacitor package for the 2510 is the trickiest of the bunch. Size and voltages need more attention than every other kit I have.

    Now regarding rates, on your last project ...
     
    Shadetree Mechanic likes this.
  6. Low_Boy

    Low_Boy Well-Known Member

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    If you remove the clear lacquer off the wires to the toride the radio will lose power. They are a lot of fun to winde LOL
     
  7. Robb

    Robb Yup

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    What I found wrong with the 'hot speaker' issue (see my 1st post) - that is - the speaker magnet was sooo hot you couldn't touch it - turned out to be a 470uf/10v cap at IC103. It had no capacitance on the tester, but had about ~16 ohms of resistance.
     
    #7 Robb, Feb 6, 2018
    Last edited: Feb 6, 2018
  8. Robb

    Robb Yup

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    Not the same guy. I had also set up a 29 LTD for this guy's son just last week. That one was a real turdlocker; works well now.
     
    #8 Robb, Feb 6, 2018
    Last edited: Feb 6, 2018
  9. loosecannon

    loosecannon Sr. Member

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    use GC electronics Radio TV solvent for the glue.

    remove the coils from the radio and soak them in some solvent for a minute or two, then use a brush to brush off the now softened glue.

    works like a charm.

    for other areas of the radio, just drip small amounts of the solvent on the glue over the span of a few minutes and then pick it off.
    remember that it can get underneath components and you may have to remove them to check for glue.

    use a product called "Barge" contact cement for the new glue.


    the items that Nomad uses are basically the same things as these.

    And Robb, you could save you customer some money if you just get the cap kit from China.

    LOL Just Kidding!!
    (that one was for you KM)

    LC
     
    Robb likes this.
  10. ExitThirteen

    ExitThirteen Grumpy and Cranky

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    You can replace the MRF477 final with a C1969. You will need to swap the collector and emitter legs when you install it, so just use a small piece of heat shrink tubing on one of the legs when you cross them. Make sure to use a mica or ceramic insulator when installing the C1969 to the heatsink. Remove the (2) paralleled 560pf disc caps from where the old final was soldered in. Re-bias the C1969 to 50-60mA. Done. Will net you about 18-22W PEP on SSB. Been doing this mod for years and it works great.


    ~Cheers~
     
    Robb likes this.
  11. Robb

    Robb Yup

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    Good idea; might end up doing just that.
    Think I remember forum member sp5it saying that he replaced the final with a 2SC1945. Uses the same pinout IIRC. But not a real option, since it is hard to find a real one among all of the fakes.
     
  12. Chevboy0167

    Chevboy0167 Active Member

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    Say Robb... I have an original Blue dot MRF477 here that is a pull from a dead rig that shows hfe of 27 if you're interested?
     
  13. Low_Boy

    Low_Boy Well-Known Member

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    2sc 1945 transistors are getting harder to find and are harder to find then the mrf 477 or mrf 497. I turned up nothing but Chinese counterfeits for the 2sc 945
     
    #13 Low_Boy, Feb 6, 2018
    Last edited: Feb 6, 2018
  14. kopcicle

    kopcicle Well-Known Member

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    Nomad and I have touched on this before. As an exercise for the curious open the radio and find the collector of the MRF477. Now without turning the radio on put power to it . Now measure the voltage at the collector of the transistor.

    Then attach the B+ where it normally goes and attach the ground to the chassis . Now turn the radio on.

    First, the front panel switch simply can not handle the current for the entire radio. The power switch just turns the receiver off and on. There is always power to the driver and final. A relay with suitable contacts , well, figure it out :)

    I've not had any issues with case ground being board ground. In' fact I've first tried replacing "isolation" caps before just bus wiring across to get rid of crap in the receiver. I don't remember finding what was causing the crap as I had a customer budget to meet and it was beer thirty.

    There are all kinds of things that can go wrong with a 2510 that are directly related to electrolytics, almost as many as can be caused by hooking it up backwards.
    one question quiz...
    So , what happens if you put a car battery in backwards with a 2510 wired into the car?
     
    LeapFrog likes this.
  15. kopcicle

    kopcicle Well-Known Member

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    I have eight (maybe more) 2510's here in various states of customer didn't want to pay to have fixed.
    Two are obvious , a crater in the middle of the 477
    One was a modified clarifier, output of a regulator in the mezzanine to the top of the RIT and the bottom directly to ground.
    Two smoked the audio chip, easy fix, replace the audio chip only to have them come back with a smoked audio chip some time later. Quoted a recap and here they sit.
    One has the 477 replaced with a 455 stud mount. it was installed with base and collector reversed.
    One has a dead chip, clock, regulator, who knows?
    One was lighting struck, or, as hearsay goes it got tazered because the owner was a complete ass. Aside from the possible active device damage I found most of the receiver transformers open.

    I have less than no interest in fixing them. I keep my several running but as they fail it's a case of diminishing returns. Do I really want to clear my bench (or dig it out of boxes even) just to spend hours with a 25 year old radio's voltage charts ? For what ? A 10, 11, 12m 30 watt multimode radio ? Keep in mind I have "several" general coverage radios with and without VHF/UHF so my opinion may differ from some.
     

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